Why is this exponential (or geometric - a
curved line) rather than linear (or arithmetic - a straight
line)? Every month, the reproductive base gets larger!

III. Limits to Population
Growth

Two major themes govern the growth of
populations over time:

1. The resources of an
environment control the growth and continued existence of
populations2. The resources of an environment are
limited

Few populations can live up to their biotic
potential = where conditions are ideal, every member has
food, shelter, no predators or pathogens in the environment,
maximum reproduction. Limiting factors in the environment
on food, water, minerals, predators, shelter, buildup of waste
materials usually prevent organisms from reaching their biotic
potential

Carrying capacity: maximum number of
individuals an environment's resources can sustain

Typically, after a period of exponential
growth, growth levels off or even stops when the carrying
capacity is reached

You decide: which country is the most overpopulated in
terms of resource consumption and creation of environmental damage? See
more at Population
and the Environment

U.S.A.

India

Production /
consumption of goods & services

21%

1%

Use of world's
non-renewable resources

25%

3%

Creation of world's
trash and pollution

25%

3%

Percent of world's
population

5%

~280 million

16%

~1.10 billion

7. Sustaining the masses:

Our
staggering population growth continues even though worldwide 2,000,000,000
people live in abject poverty (malnourished or starving, without clean water,
sewage treatment, medical treatment, or shelter)

Every day, ~24,000 - 40,000 people die from starvation.
WHY? - when there is enough food already on the planet to feed everyone? ...what
are some of the real
issues behind hunger? [Image]

Many governments are trying to lower birth rates through family
planning programs.

Average "replacement rate" of ~2 children per
couple

But, even if each couple on the planet decided TODAY to
have only 2 kids, the human population would keep growing for another 60
years because of all the young people around today who will one day reach
reproductive age! (Currently, more than 33% of the world's population
is in the pre-reproductive state!)

Today: total fertility rate in the US - 6.5 in 1950and 3.1 in 1995

A country's age structure tracks the
number of prople in the pre-reproductive, reproductive, and
post-reproductive years. Age structures for a few countries: